\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{circuitikz}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\ctikzset{bipoles/length=1cm}
\begin{document}
\small
\begin{circuitikz}[>=latex, scale=1.0,european]
  % \useasboundingbox(0.9,0)rectangle(5.1,5);
  \draw (-2,0) to [R=$R_1$, *-*] (0,0) to  [R=$R_2$, *-*] (2,0);
  \draw (-2,0)--(-2,1.2) to [rmeter, t=G] (2,1.2)[-o]--(2,-1.0)node[above right]{$c$};
  \draw [-o](0,0)--(0,-1.0)node[above right]{$b$};
  \draw [-o](-2,1.2)--(-2,-1.0)node[above right]{$a$};
  \node at (0,-1.0)[below]{\qty{1}{A}}; \node at (0,0.9)[below]{$R_3$};
  \node at (2,-1.0)[below]{\qty{0.1}{A}};
  \draw [dashed](2.5,1.7) rectangle (-2.5, -0.5);
\end{circuitikz}
\end{document}